Experimental evaluation of thermal properties of autoclaved aerated concrete at high temperature

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.

In the study of the mechanical behaviour of building materials in presence of fire, the knowledge of the correlation of the thermal conductivity and of the specific heat with temperature is of fundamental importance. The numerical verifications of fire resistance of structures are often carried out using computer codes that solve differential equations of thermal exchanges. For the correct prediction of the evolution with the temperature, the knowledge of the above thermal properties as a function of temperature is required. The measurement of thermal conductivity and thermal diffusivity has been made with the Hot Disk Thermal Constants Analyser equipment. This apparatus, that operates in variable speed, generates a thermal constant power in a nickel sensor placed in contact with two specimens of the same material. It allows the detection of temperature increase on the surfaces of these specimens. Assuming as infinite the specimens size, the solution of the general equation of the heat conduction allows to express the temperature increase in of the specimen as a linear dimensionless time function; the simultaneous determination of thermal diffusivity and conductivity of the test material becomes easy. The experimental environment suitable to achieve high temperatures consists of a special controlled temperature oven in which measurements are made with sensors enclosed in two layers of refractory material (mica) suitable for working with acceptable accuracy in a range of temperatures between 500- 1000 K. This paper presents the results of experimental measurements of thermal conductivity and of volumetric specific heat, r cp, carried out at high temperature on autoclaved aerated concrete (AAC) specimens at different densities. The results are also compared with the directions on the material provided by national and international standards.